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L M Rodrigues

Publications and source records attributed to L M Rodrigues.

At least 37 records · Page 2Linked to original sources
PubMed1998

Magnetic resonance imaging techniques for monitoring changes in tumor oxygenation and blood flow.

The application of functional magnetic resonance (MR) imaging techniques to the measurement of oxygenation and blood flow in tumors is described. Gradient recalled echo MR imaging (GRE-MRI) offers a real-time noninvasive method for monitoring tumor response to vasomodulators such as carbogen (95% O2/5% CO2) breathing in attempts to overcome tumor hypoxia and improve treatment efficacy. Although the response is tumor-type dependent, increases in signal intensity of up to 100% have been observed in several animal tumor types. Responses are also seen in human tumors. The observed increases in GRE-MRI signal intensity are due to a combination of a reduction of deoxyhemoglobin in the blood causing changes in the MR imaging relaxation time T2* and changes in blood flow and may also reflect the capillary density. Thus, the magnitude of the GRE image intensity change gives an indication of the potential response of an individual tumor to treatments that aim to improve tissue oxygenation and therefore how the tumor may respond to therapy. In addition, carbogen breathing by the host has been shown to increase the uptake and efficacy of chemotherapeutic agents in animal tumors.

Administration, Inhalation↗
PubMed1998

The effects of host carbogen (95% oxygen/5% carbon dioxide) breathing on metabolic characteristics of Morris hepatoma 9618a.

Characteristics of the tumour metabolic profile play a role in both the tumour-host interaction and in resistance to treatment. Because carbogen (95% oxygen/5% carbon dioxide) breathing can both increase sensitivity to radiation and improve chemotherapeutic efficacy, we have studied its effects on the metabolic characteristics of Morris hepatoma 9618a. Host carbogen breathing increased both arterial blood pCO2 and pO2, but decreased blood pH. A fourfold increase in tumour pO2 (measured polarographically) and a twofold increase in image intensity [measured by gradient recalled echo magnetic resonance (MR) imaging sensitive to changes in oxy/deoxyhaemoglobin] were observed. No changes were seen in blood flow measured by laser Doppler flowmetry. Tumour intracellular pH remained neutral, whereas extracellular pH decreased significantly (P < 0.01). Nucleoside triphosphate/inorganic phosphate (NTP/Pi), tissue and plasma glucose increased twofold and lactate decreased in both intra- and extracellular compartments, suggesting a change to a more oxidative metabolism. The improvement in energy status of the tumour was reflected in changes in tissue ions, including Na+, through ionic equilibria. The findings suggest that the metabolic profile of hepatoma 9618a is defined partly by intrinsic tumour properties caused by transformation and partly by tissue hypoxia, but that it can respond to environmental changes induced by carbogen with implications for improvements in therapeutic efficacy.

Administration, Inhalation↗
PubMed1997

A pharmacokinetic and pharmacodynamic study in vivo of human HT29 tumours using 19F and 31P magnetic resonance spectroscopy.

19F-MRS (magnetic resonance spectroscopy) was used to study the pharmacokinetics of 5-fluorouracil (5-FU) in human (HT29) tumour xenografts, with and without pretreatment of the mice using either thymidine (40 min) or interferon-alpha (2 and 24 h). A 200 mg/kg i.p. bolus dose of 5-FU was eliminated from control tumours with a t1/2 of 25.4 +/- 2 min (mean +/- SEM, n = 11), while both thymidine (500 mg/kg) and interferon (50,000 IU/mouse) significantly increased t1/2 to 36.5 +/- 6.1 (n = 5) and 48.1 +/- 13.6 min (n = 4), respectively (P = 0.04, Gabriel's ANOVA). Thymidine increased 5-FU anabolism to cytotoxic 5-fluoronucleotides, and decreased the amount of tumour catabolites; the latter probably recirculated from liver since isolated HT29 cells did not catabolize 5-FU. These in vivo observations were confirmed by 19F-MRS quantification of tumour extracts. Interferon did not significantly affect 5-FU metabolism in the tumour or liver, nor the 5-FU t1/2 in liver. Treatment of tumours with 5-FU or interferon had no effect on tumour growth, whereas the combination strongly inhibited growth. 31P-MRS of HT29 tumours showed that 2 and 24 h after i.p. injections of interferon there was a significant increase in the pHint of 0.3 +/- 0.04 units (P = 0.002), while pHext and the tumour NTP/Pi ratio were unchanged. The large increase in the negative pH gradient (-delta pH) across the tumour plasma membrane caused by interferon suggest the delta pH may be a factor in tumour retention of 5-FU, as recently shown in isolated tumour cells.

Animals↗
PubMed1997

In vivo detection of ifosfamide by 31P-MRS in rat tumours: increased uptake and cytotoxicity induced by carbogen breathing in GH3 prolactinomas.

The direct detection and monitoring of anti-cancer drugs in vivo by magnetic resonance spectroscopy (MRS) may lead to improved anti-cancer strategies. 31P-MRS has been used to detect and quantify ifosfamide (IF) in vivo in GH3 prolactinomas and N-methyl-N-nitrosourea (MNU)-induced mammary tumours in rats. The average concentration of IF in the GH3 prolactinoma over the first 2 h following a dose of 250 mg kg-1 i.v. was calculated to be 0.42 micromol g-1 wet weight, with a half-life of elimination (t1/2) of 2-4 h. Carbogen (95% oxygen/5% carbon dioxide) breathing increased the amount of IF taken up by the GH3 prolactinoma by 50% (P<0.01) to 0.68 micromol g-1 wet weight, although t1/2 elimination rates were unchanged. IF was also detected in the liver in vivo, with a t1/2 of about 1 h. Carbogen breathing did not affect the maximum peak area (Cmax) or the t1/2 in the liver. Most importantly, the carbogen-induced increase in IF uptake by the tumour caused significant growth delay at all time points in the GH3 tumour growth between day 5 and day 12 (P< 0.01) compared with IF alone. These findings show that carbogen breathing has potential for increasing the efficacy of anti-cancer drugs. Isolated GH3 cells were sensitive to the parent drug (IF) in vitro (IC50 = 1.3 +/- 0.2 mM) suggesting that the GH3 cells may be either expressing P450 enzymes or are sensitive to the parent drug per se.

Animals↗
PubMed1997

The response to carbogen breathing in experimental tumour models monitored by gradient-recalled echo magnetic resonance imaging.

Gradient-recalled echo magnetic resonance imaging (GRE MRI), which gives information on blood flow and oxygenation changes (Robinson SP, Howe FA, Griffiths JR 1995, Int J Radiat Oncol Biol Phys 33: 855), was used to observe the responses of six rodent tumour models to carbogen breathing. In one transplanted rat tumour, the Morris hepatoma 9618a, and a chemically induced rat tumour, the MNU-induced mammary adenocarcinoma, there were marked image intensity increases, similar to those previously observed in the rat GH3 prolactinoma. In contrast, the rat Walker carcinosarcoma showed no response. In two mouse tumours, the RIF-1 fibrosarcoma and the human xenograft HT29, carbogen breathing induced a transient fall in signal intensity that reversed spontaneously within a few minutes. The rat GH3 prolactinoma was xenografted into nude mice, and an increase in image intensity was found in response to carbogen, suggesting that any effects that carbogen may have had on the host were not significant determinants of the tumour response. The increases in GRE image intensity of the MNU, H9618a and GH3 tumours during carbogen breathing are consistent with increases in tumour oxygenation and blood flow, whereas the responses of the RIF-1 and HT29 tumours may be the result of a transient steal effect followed by homeostatic correction.

Administration, Inhalation↗
PubMed1996

31P-magnetic resonance spectroscopy studies of nucleated and non-nucleated erythrocytes; time domain data analysis (VARPRO) incorporating prior knowledge can give information on the binding of ADP.

Human erythrocytes have no nucleus, mitochondria or endoplasmic reticulum, whereas chicken erythrocytes have a nucleus and mitochondria and are closer in internal morphology, to cells such as the hepatocyte. Erythrocytes were used to test the hypothesis that 31P-MRS invisibility of ADP is associated with the presence of intracellular organelles. Simple frequency domain spectral analysis methods showed that all the acid extractable ADP (and ATP) was MR-visible in human erythrocytes. However, such methods gave variable estimates for 31P-NMR spectra of fresh chicken erythrocytes from which no conclusions could be drawn about the MR-visibility of ADP. Only when the data were fitted by a method incorporating prior knowledge of the ATP and ADP peak structure, using the time domain VARPRO method, was it possible to conclude that in fresh chicken erythrocytes, similar to other nucleated cells (liver, muscle), all the acid extractable ADP appeared to be MRS invisible, indicating binding or sequestration by intracellular organelles.

Adenosine Diphosphate↗
PubMed1996

The acute and chronic effects of alcohol upon cardiac nucleotide status.

The aim of the investigation was to ascertain the biochemical and morphological basis for the functional impairments in the heart due to alcohol. In chronic studies rats were fed a nutritionally complete liquid diet containing 35% of total calories as ethanol, controls were pair-fed identical amounts of the same diet in which ethanol was replaced by isocaloric glucose. In acute studies rats were injected with ethanol at a dose of 75 mmol/kg body weight. Pre-treatment of acute ethanol-dosed rats with cyanamide (ALDH inhibitor) was designed to raise acetaldehyde levels. In chronic studies ventricular adenine nucleotides, ATP, ADP and AMP; NAD(+), ATP ratios and the energy charge showed no alteration after 6 weeks of alcohol feeding. Light and electron microscopy sections indicated very little structural damage to muscle fibres and organelles (especially the mitochondria) in both atria and ventricles. Ventricular fibre diameters, throughout the different ranges, showed no significant differences between chronically alcohol and control-fed rats. In acute studies an increase in ventricular AMP levels (micromoles/g wet weight) occurred following cyanamide and cyanamide + ethanol treatment (+57%, p < 0.025 and +76%, p<0.01, respectively), but not as a consequence of ethanol alone. Cyanamide+ethanol caused marked elevation in ADP levels (+28%, p < 0.05) and again ethanol was without effect. ATP and GTP levels were not altered by any of the acute treatments. The energy charge was slightly reduced in both cyanamide and cyanamide+ethanol groups (-8%, p < 0.01 and -7%, p < 0.05, respectively), but not by ethanol alone. In conclusion, chronic alcohol appears to have minimal effects upon cardiac nucleotides which suggest that possible adaptive mechanisms are induced during the 6-week period and that alternative pathways other than defects in adenine nucleotide concentrations are involved in the pathogenesis of AHMD. The acute study suggests that the heart is resilient to toxic levels of alcohol and acetaldehyde in terms of ATP and GTP levels, despite the elevated AMP, ADP and GDP levels.

Journal Article↗
PubMed1995

In vivo 31P MRS: absolute concentrations, signal-to-noise and prior knowledge.

Absolute metabolite concentrations have been estimated for nucleoside triphosphate and P(i) from in vivo 31P MR measurements using ISIS localization in a rat tumour model, and the results have been compared to those obtained from acid extracts of the tumours. The aim of the experiment was to assess the performance of four different spectral analysis techniques used for absolute quantitation. The spectral analysis techniques used were two frequency domain methods (peak area integration and Lorentzian fitting--FITSPEC) and two time domain methods (VARPRO and HLSVD). The spectra were acquired in blocks so that the degradation in performance of the four spectral analysis methods with decreasing signal-to-noise ratio (SNR) could be compared and referenced. This and the inclusion of a sophisticated method incorporating prior knowledge yields a more realistic and comprehensive protocol than previously published comparisons. The results suggest that VARPRO is the method of choice for quantitative analysis of tumour 31P MR spectra, giving the most reliable results at low SNR.

Animals↗
PubMed1995

The effect of blood flow modification on intra- and extracellular pH measured by 31P magnetic resonance spectroscopy in murine tumours.

Intra- and extracellular pH (pHi and pHe) were measured simultaneously by 31P magnetic resonance spectroscopy (MRS) in CaNT tumours before and after blood flow modification. Before modification, pHi was 7.1 +/- 0.09 (n = 11) and pHe [measured with an MRS-visible extracellular marker, 3-aminopropyl phosphonate (3-APP)] was 6.7 +/- 0.05 (n = 8). Chemical shift imaging and localised MRS experiments showed that the 3-APP signal was only from the tumour, not surrounding tissue. After modification by vascular occlusion, independent of whether tumours were maintained at room temperature (22-24 degrees C) or kept warm (33-35 degrees C), there was a decrease in pHi and pHe with pHi decreasing to a greater extent. Qualitatively similar results were found using flavone acetic acid (FAA) as a blood flow modifier; only four out of nine tumours responded to FAA. Concomitant with the reduction of the pH gradient after modification was a decrease in the phosphorylation state of the adenine nucleotides measured either as ATP/Pi by MRS or [ATP]/[ADP][P(i)] in tumour extracts. These results indicate that the intracellular uptake of chemotherapeutic drugs which are dependent on the transmembrane pH gradient will not be enhanced in cells made ischaemic as a result of vascular shutdown.

Adenosine Triphosphate↗
PubMed1993

Effect of acute ethanol dosage on nucleotide levels in the rat jejunum: relationship to protein synthesis.

The effects of an acute dose of ethanol (75 mmol/kg body weight; i.p.) on nucleotide levels in the rat jejunum were investigated. After 2.5 hr, ethanol exposure significantly reduced ATP and GTP contents and increased ADP and GDP contents. There were no statistically significant effects on pyrimidine nucleotides or IMP. Fractional rates of jejunal protein synthesis were also significantly reduced by ethanol. It was concluded that purine nucleotides are sensitive to acute ethanol administration in the rat jejunum. This may explain why rates of protein synthesis are decreased in the jejunum, as these nucleotides play a key role in polypeptide formation.

Alcoholic Intoxication↗
PubMed1990

Monitoring tumor growth and regression by 31P magnetic resonance spectroscopy.

Magnetic resonance spectroscopy (MRS) uniquely provides noninvasive access to chemistry in vivo. 31P MRS can be used to monitor the high energy phosphates--phosphocreatine (PCr) and ATP, and their breakdown product--Pi, in situ in animals or patients. In several experimental tumor lines in animals it has been shown that the PCr/ATP and other related ratios steadily decline as the tumor increases in size, and that this effect is reversed when the tumor is treated with a therapeutic modality to which it responds. Acid extracts of freeze-clamped tumors at different stages of growth have confirmed these MRS observations and give additional information on related compounds such as creatine and ADP. Results show that, in the tumors studied, at least 80% of the ADP and about 40% of the Pi are bound and not in solution in the cytosol. Histological sections have indicated that the MRS response to endocrine therapy, in an NMU-induced estrogen-sensitive mammary tumor model, precedes any histological changes or any measurable regression. If these findings can be translated into a clinical setting, this may mean that MRS can be used in the clinic as an early predictor of tumor responsiveness to treatment. In untreated tumor growth, the cause of the decrease in PCr and ATP relative to Pi is probably due to the tumors outgrowing their blood supply and the cells becoming increasingly hypoxic. The PCr is lost more rapidly than ATP, indicating that the equilibrium in the creatine kinase reaction is maintained in these tumors. When the tumor is treated, cellular growth ceases and the requirement for oxygen and other nutrients is greatly reduced. This would allow the cellular energy reserves to be repleted and thus lead to the paradoxical improvement in the high energy phosphate status of a tumor that is about to regress.

Adenine Nucleotides↗
PubMed1990

31P-NMR spectroscopy and histological studies of the response of rat mammary tumours to endocrine therapy.

We have shown by 31P-NMR spectroscopy that ovariectomy, in N-methyl-N-nitrosourea induced mammary adenocarcinomas, increases signals from phosphocreatine (PCr) relative to nucleoside triphosphate (NTP) before measurable regression (2 days) and for at least a further 13 days. The present study correlates the NMR changes with histological changes in the regressing tumour. Mammary tumours were examined by NMR before, and 2 and 14 days after, ovariectomy or sham-ovariectomy. Sections were taken from five tumours at each time point after operation for histology and for immunocytochemical staining of myoepithelial cells, luminal cells and basement membrane material. The histology showed typical cribriform papillary type mammary adenocarcinomas. The luminal cell population had a high mitotic activity and there was a prominent myoepithelial layer. At 2 days post-ovariectomy no significant change in mitotic activity was observed and no cytological characteristics attributable to ovariectomy could be seen. At 14 days postovariectomy the tumour was indistinguishable from a tubular adenoma, had significantly reduced mitotic activity, a relative increase in myoepithelial cells and basement membrane material. The changes detected by NMR must reflect early metabolic events, perhaps related to the histological changes observed at 14 days after ovariectomy. 31P-NMR spectroscopy may permit early monitoring of endocrine therapy for mammary cancer.

Adenocarcinoma↗
PubMed1989

Potential artefacts from overlying tissues in 31P NMR spectra of subcutaneously implanted rat tumours.

31P spectra of rat tumours obtained with surface coils are shown to include skin signals of varying intensity. As reported previously by Stubbs, M., Rodrigues L. M., and Griffiths, J. R., (NMR in Biomedicine 1, 50-55, 1988) three hepatomas (rapidly growing Morris hepatoma 7777 and slow growing 9618A, and the UA hepatoma) had negligible phosphocreatine (PCr) or creatine (Cr) in acid extracts but frequently had PCr signals in surface coil spectra. Prolactinomas and mammary adenocarcinomas, which had significant PCr and Cr in extracts, showed higher PCr/NTP ratios in spectra taken in vivo than in extracts. A phantom for studying skin signals in vivo is described. A glass sphere of typical tumour size (3-4 mL) is implanted subcutaneously in the rat. Variations in skin signal with pulse duration are demonstrated with this phantom. The factors that could contribute to skin artefact in 31P tumour spectra include: (i) the relative concentrations of metabolites in skin and tumour; (ii) the skin thickness, which depends on the implantation site and rat size; (iii) skin invasion by the tumour; (iv) coil design (solenoid coils and Faraday shields are unlikely to eliminate this problem); (v) pulse repetition times; (vi) pulse duration and other NMR parameters. Careful attention to these factors could reduce skin artefacts.

Adenocarcinoma↗
PubMed1989

Growth studies of subcutaneous rat tumours: comparison of 31P-NMR spectroscopy, acid extracts and histology.

31P-NMP, surface coil spectra of three subcutaneously implanted rat tumours (Morris hepatoma 7777, GH3 prolactinoma, Walker carcinosarcoma) and an N-methyl-N-nitrosourea induced rat mammary adenocarcinoma at different stages of growth were obtained and compared with histological sections taken immediately after NMR acquisitions. Metabolite ratios (phosphocreatine (PCr)/beta nucleoside triphosphate (beta NTP), PCr/Pi, beta NTP/Pi) calculated from the NMR spectra were compared with ratios obtained from acid extracts of tumours of similar size. Measurements of creatine and ADP were also made. Three of the tumours showed positive correlations between increasing tumour size and decreasing metabolite ratios measured both by NMR and in extracts, whereas the Walker carcinosarcoma showed no correlation between size and any parameters measured. Phosphorus metabolite ratios, measured in extracts of skin overlying the tumours, indicated a fall in high energy phosphate when there was histological evidence of skin invasion by the tumour. Surface coil 31P-NMR spectra of subcutaneously grown or induced tumours in the rat represent a slowly changing steady state as the tumour increases in size. We conclude that increasing numbers of hypoxic tumour cells, rather than large areas of necrotic tissue, contribute largely to the NMR spectrum.

Adenocarcinoma↗
PubMed1988

31P-nuclear magnetic resonance spectroscopy studies of the response of rat mammary tumors to endocrine therapy.

We have used 31P-nuclear magnetic resonance spectroscopy to detect the metabolic changes that occur in estrogen-sensitive, N-methyl-N-nitrosourea-induced rat mammary tumors as they regress following ovariectomy. In untreated animals the spectra of the tumors showed a steady loss of high energy phosphates (phosphocreatine and nucleoside triphosphates) and an increase in inorganic phosphate. This was reversed after ovariectomy. Spectral changes occurred before detectable regression of the tumor. Estrogen-insensitive tumors, grown from implanted Rama 600 and 622 cells, did not regress in response to ovariectomy, and their high energy phosphates continued to fall; estrogen-sensitive tumors also failed to respond to sham ovariectomy. These effects are probably due to the reduction in cellular energy requirements that occurs when the hormonal stimulus to growth is removed. Because the nuclear magnetic resonance method is noninvasive, this technique should be applicable clinically as a means of predicting the response of a tumor to endocrine therapy.

Adenosine Triphosphate↗
PubMed1988

Phosphate metabolites in rat skin.

A model for studying the 31P NMR spectrum of rat skin without contribution from other tissue signals has been developed by creating a skin pedicle. 31P NMR spectra were obtained with a solenoidal coil, which was separated from the flank of the rat by a Faraday shield. Phosphomonoesters, inorganic phosphate (Pi) (1.63 +/- 0.12 mumols per g wet wt), phosphodiesters, phosphocreatine (PCr) (1.4 +/- 0.12 mumols per g wet wt) and ATP (1.35 +/- 0.22 mumols per g wet wt) were observed, superimposed on broader signals, probably due to phospholipids. Extracts of freeze-clamped pedicles contained concentrations of phosphorus metabolites similar to those seen by NMR. The exception was Pi which was twofold higher in the extract. The presence of the broader phospholipid contribution suggests that the signals did not arise solely from the panniculus carnosus muscle of rat skin, although this muscle was evident on histological examination of the pedicles. In extracts of normal rat skin levels of creatine, ATP, ADP and Pi were similar to those of pedicles, whereas PCr was about twofold higher. Signals from rat skin are likely to contribute to spectra of subcutaneous organs and tumours. Two kinds of rat hepatoma that contained no PCr frequently gave PCr signals from the overlying skin, whereas in three other subcutaneous tumours the contribution from skin was negligible.

Adenosine Diphosphate↗